This invention is directed to a direct-injection spark-ignition type engine control apparatus for correcting engine torque based on engine operating conditions.
It is conventional practice to realize a desired target torque (for example, during a gear shift operation made in an automatic transmission) using feedback control of the intake air flow rate in a manner to converge the engine torque to the target torque while correcting the spark timing according to a difference between the engine torque and the target torque. In order to achieve the target torque, the torque control (torque correction), which requires a faster response than intake air flow rate control can provide, is made by correcting spark timing, as discussed in Japanese Patent Kokai No. 5-163996.
In recent years, direct-injection spark-ignition type engines have attracted special interest. In such a direct-injection spark-ignition type engine, it is the current practice to make a combustion mode change, according to engine operating conditions, between homogeneous combustion (wherein fuel is injected during an intake stroke to diffuse the injected fuel so as to form a homogeneous mixture in the combustion chamber) and stratified combustion (wherein fuel is injected during a compression stroke to form a stratified fuel mixture around the spark plug) as discussed in Japanese Patent Kokai No. 59-37236.
With such a direct-injection spark-ignition type engine, sparks must be produced at a time when the mixture is close to the spark plug if torque correction is to be made by the use of spark timing during stratified combustion. However, the range over which spark timing can be corrected is too narrow to permit sufficient torque correction during stratified combustion. An attempt to correct spark timing to an excessive extent will cause degraded combustion performance and eventually misfire.